Fusible resistor



March 16., 1954 FIGJ.

O. F. FISHER 2,672,542

FUSIBLE RESISTOR Filed Feb. 2, 1952 INVENTOR.

AT TORNEYS;

Patented Mar. 16, 1954 UNITED STATES ATENT OFFICE FUSIBLE RESISTOR Application February 2, 1952, Serial No. 269,668

4 Claims. l

This invention relates to a fusible resistor and has particular reference to a resistor which will operate both as a resistor and fuse.

IOne object of the invention is to provide a combination resistor and fuse at relatively low cost.

Another object is to provide a resistance unit which under normal electrical load will operate as a resistor only but which when subjected to an overload of current will sustain the load for lished within closely controlled limits.

These and other objects of the invention will appear hereinafter in connection with the following description of the drawing in which:

Fig. l is a front elevational view of a fusible resistor illustrating an embodiment of the invention; Y

Fig. 2 is a view similar to Fig. 1 with the nal coating applied to the resistor;

Fig. 3 is a front elevational View of another embodiment of the invention;

Fig. 4 is a rear elevational View of still another embodiment of the invention;

Fig. 5 is a section taken on line 5-5 of Fig. 2, and

Fig. 6 is a section taken on line 6-6 of Fig. 4.

Referring to the embodiment of the invention illustrated in Fig. 1 there is shown a resistor which in general comprises a base or core I upon which is wound a number of turns of resistance -wire 2. Wire 2 is clamped at each end to base I by clamps 3 from which extend the terminals 4. Terminals A are connected into the electrical circuit, not shown, with which the resistor is employed.

Base I may be a solid or a relatively flexible dielectric and heat-resistant material such as of asbestos, clay or mica. The thickness and size of the base of the resistor will, of course, be varied depending upon the usage to which the resistor is to be put.

The turns of resistance wire 2 and the diameter of the wire and the metal or alloy of which wire 2 is made depends upon the value of the resistance required for the particular electrical r as a small rectangular shaped piece of asbestos which has been cemented'to one side of base I and lies over some of the turns of resistance wire 2 approximately in the center of the resistor. The material 5 might also be a blob of a paste or plastic, such as asbestos paste or the like, and in an event should be of a nature wherein upon drying the material is secured in and of itself to base I or be a material capable of being cemented or otherwise secured to base I. n

The -asbestos covering 5 shown has been found particularly adaptable since its thickness and size can be readily fixed and in this manner the time lag for the fusing or melting of resistance wire 2 upon overload of electric current can be controlled within dened limits. The cement for securing the asbestos material 5 to base I is not shown, but it also should be a dielectric and capable of withstanding moisture and heat.

Normal electrical load is carried by the resistor, but when an electrical overload occurs the ensuing heat that develops in wire 2 is trapped between base I and material 5 resulting in an intense concentration of heat at temperatures high enough to ultimately melt those portions of resistance wire 2 beneath material 5. The electrical load above normal is sustained by wire 2 over a predetermined length of time and then the wire will melt within a predetermined time after the described initial period of time has elapsed. For example, the overload of current may be sustained for a period of thirty seconds and then wire 2 will fuse Within the next period of thirty seconds and break the circuit. Thus, damage to other parts connected into the circuit will be eliminated by the fusing of the resistor within an established length of time of overload.

The construction of the resistor is completed by a suitable coating 6, as illustrated in Figs. 2 and 5, which covers the entire resistor on both sides of base I including clamps 3, resistance wire 2 and heat-insulating material 5. Coating 6 is of a material such as an electric cement or a ceramic which readily emits heat and tends to resist moisture.

Fig. 3 illustrates a resistor wherein the two resistance wires 1 are not wound about base 8 but rather extend longitudinally of the base and are clamped thereto at the ends by clamps 9 from which terminal wires I0 extend. Wires 1 are covered 'at the center of the unit by a material II which corresponds to the material 5 previously described. The base of the resistor and the resistance wire used also correspond to those described with respect to Fig. 1.

Fig. 4 illustrates a resistor which has a generally short base I2 around which resistance wire I3 is wound so that the clamps III from which terminal wires I5 extend are near the center of the base or core I2. In this embodiment, the heat-insulating material I6 lying over resistance wire I3 is shown as secured to base I2 entirely aroundf the entire unit. In this construction the clampsi I4 and terminal wires I5 tend to dissipate the heat from the resistor wire which is developed in service under normal electrica load. Ordinarily it has been found that the. best fusing results will be obtained under most conditions if the heat-insulating materiali4 is disposed only over one side ofthe resistor.. The: resistor of Fig. 4 is completed by the outer coating I1 as shown there and in Fig. 6. The parts described with respect to Fig. 4 and Fig. 6 correspond in materials and physical characteristics to those described with respect to Fig. l.

The invention provides a combination. resistor and fuse in which the tusing of, the resistor on overload can bey established within closely controlled time limits to break the electrical circuit invihilchy the resistor is; employed;

Employing a resistor as. both a resistor and fuse eliminates separate. connectionsfor the fuse in an electrical. circuit anda separate fusingl unit.

Variousl embodimentsv of theA invention may be employed within the scope of the accompanying claims.`

I claim:

1... In= av fusible resistonabase of heat-resistant dielectric material,` resistance wire Wrapped varound said basev fromsubstantially one end to the other, means at each` end. ofthe resistor securing. the ends of the Wire to the base and for connecting the Wire to an electrical circuit, and heat-insulating materialy secured to. one side of said` base overa portion of the resistance wire to.. retain heat in the-Wire abovenormalelectrical load. and4 fuse the wire in a predetermined length of; time tofbreak the circuit.

2 A fusi-ble resistor,y which comprises a base yit heat-resistant, dielectric material, resistance wire wrapped around said base from substantially one end to the other, clamps at each end of the base securing the ends of the wire to the base with terminal conductors for connecting the clamps to an electrical circuit, a piece of asbestos cemented to one side of said base over a portion of the resistance wire to retain heat in the wire above normal' electricalr load andl fuse'` the wire in a predetermined length of time to break the circuit, and a protective insulating coating covering the entire resistor unit.

3.` A fusible resistor, which comprises a base of'heat-resistant dielectric material, a pair of resistancc.v wire extending lengthwise of `the base in parallel. relation to each other with terminal clamps at each end of the base securing the ends of. the wire toV the base and for connectingl the wire to an electrical circuit, a piece of insulation secured to one side of the base over a portion of the wire to retain heat in the wire above normal electrical load: and fuse the wire inV a predetermined length of time to break the circuit, and a protective insulating coa-tingy covering the entire resistor.

4. A fusible resistor, which comprises a; base of heat-resistant dielectric material, resistance wire.- extend-ing. over said baseA with. terminal clamps at each end of the. base securing the ends of the Wire to the base and for connecting the wire to an electrical circuit, heat-insulating material extending around they base between, the terminal clamps and secured tothebase to cover a portionA of theresistance wire on each. side of the base and thereby retain heat in. the wire above normal electrical loadr to fuse the wire, in a predetermined lengthy of time and break the circuit, and a protective` insulating coating covering the entire` resistor.

OAKLEY. F. FISHER.

References Cited in the fileA of this, patent UNITED STATES PATENTS Number 

